According to the conventional method of writing data to a magneto-optical disk medium, as shown in the timing chart of FIG. 1, for instance, erasure of data from the magneto-optical disk medium starts as shown in (b) of FIG. 1 after transfer of writing data (data to be written) from a host to a magneto-optical disk unit is completed as shown in (a) of FIG. 1. When the data erasure is completed, writing of data to the magneto-optical disk medium is started as shown in (c) of FIG. 1. When the data has been written, verification of the written data is started as shown in (d) of FIG. 1. By the completion of the verification, the data writing is completed.
The timing charts of FIGS. 2 and 3 show a well-known data writing method as a method for reducing time for data writing in the timing chart of FIG. 1. This method is disclosed in Japanese Laid-Open Patent Application No. 5-324217.
FIG. 2 shows the case where erasure of data from a storage medium is completed after transfer of writing data is completed. In the timing chart of FIG. 2, when transfer of data from a host to a magneto-optical disk unit is started as shown in (a) of FIG. 2, erasure of data from a magneto-optical disk medium is started as shown in (b) of FIG. 2. When the data erasure is completed, writing of data to the magneto-optical disk medium is started as shown in (c) of FIG. 2. When the data has been written, verification of the written data is started as shown in (d) of FIG. 2. By the completion of the data verification, the data writing is completed.
FIG. 3 shows the case where the erasure of data from the storage medium is completed before the transfer of writing data is completed. In the timing chart of FIG. 3, as in the case of FIG. 2, when the transfer of data from the host to the magneto-optical disk unit is started as shown in (a) of FIG. 3, the erasure of data from the magneto-optical disk medium is started as shown in (b) of FIG. 3. When the data transfer is completed, the writing of data to the magneto-optical disk medium is started as shown in (c) of FIG. 3. When the data has been written, the verification of the written data is started as shown in (d) of FIG. 3. By the completion of the data verification, the data writing is completed.
As shown in FIGS. 2 and 3, in the case of processing the same amount of transferred data as in the data writing of FIG. 1, the method of the prior art enables reduction in data writing time by starting data erasure (b) in synchronization with the start of data transfer (a) and starting data writing to the magneto-optical disk medium at the time of the completion of the data transfer (a) or the data erasure (b).
However, if an error occurs during the transfer of writing data in the writing control that simultaneously performs transfer of writing data and data erasure for writing as shown in FIGS. 2 and 3, the data writing operation cannot be continued so that the data erasure is immediately suspended. Part of the data existing before data writing is lost by the suspension of the data erasure. If the transfer of writing data is completed without retrying the write command from the host thereafter, the part of the data remains lost.
In many magneto-optical disk media, important data such as file management information for managing the recorded files is arranged close to each start address. Therefore, if the data close to a start address is lost by data transfer error, the magneto-optical disk medium cannot be used thereafter.
With a recent increase in the data transfer rate, the rate of occurrence of data transfer error has become higher, so that it is desired to avoid data loss caused by data transfer error.